Shengtian Wang

BIODIESEL PRODUCTION FROM HIGH ACID VALUE WASTE FRYING OIL CATALYZED BY SUPERACID HETEROPOLYACID

Transesterification of waste cooking oil with high acid value and high water contents using heteropolyacid H3PW12O40·6H2O (PW12) as catalyst was investigated. The hexahydrate form of PW12 was found to be the most promising catalyst which exhibited highest ester yield 87% for transesterification of waste cooking oil and ester yield 97% for esterification of long‐chain palmitic acid, respectively. The PW12 acid catalyst shows higher activity under the optimized reaction conditions compared with conventional homogeneous catalyst sulfuric acid, and can easily be separated from the products by distillation of the excess methanol and can be reused more times. The most important feature of this catalyst is that the catalytic activity is not affected by the content of free fatty acids (FFAs) and the content of water in the waste cooking oil and the transesterification can occur at a lower temperature (65°C), a lower methanol oil ratio (70:1) and be finished within a shorter time. The results illustrate that PW12 acid is an excellent water‐tolerant and environmentally benign acid catalyst for production of biodiesel from waste cooking oil. Biotechnol. Biotechnol. Bioeng. 2008;101: 93–100.

Single step conversion of cellulose to levulinic acid using temperature-responsive dodeca-aluminotungstic acid catalysts

The conversion of cellulose into platform chemicals is essential for the sustainable development of the chemical industry. With this aim, the single step conversion of cellulose to industrially important levulinic acid (LA) using heteropolyacids (HPAs) as catalysts has been investigated. A new series of heteropolyacids (HPAs) [(CH3)3NCH2CH2OH]nH5−nAlW12O40 (abbreviated as ChnH5−nAlW12O40, n = 0–5) have been synthesized by a precipitation/ion exchange method using choline chloride and H5AlW12O40 as precursors. The resulting HPA nanohybrids exhibited novel switchable properties based on temperature variation due to the incorporation of the choline cation, which dissolved in the reaction mixture at higher temperatures to form a homogeneous catalytic system and then precipitated spontaneously from the mixture at room temperature. The three synergistic effects of temperature-stimulus combined with its dual Lewis and Bronsted acidity endowed ChH4AlW12O40 with more efficiency for catalyzing the conversion of cellulose into glucose in water with 75.9% yield and 94.8% conversion at 140 °C for 3 h. Meanwhile, MIBK (methyl isobutyl ketone), a green co-solvent, produced the highest reported yield of LA directly from cellulose in a highly effective single phase conversion strategy, with 74.8% yield and 98.9% conversion in one pot, which is the best result compared to previous reports. Moreover, the recycling of such HPA catalysts was easily achieved without structural changes or loss of weight by lowering the reaction temperature. In addition, the conversion of cellulose to glucose could be promoted by microwave assistance.

Conversion of highly concentrated fructose into 5-hydroxymethylfurfural by acid–base bifunctional HPA nanocatalysts induced by choline chloride

A series of acid–base bifunctional heteropolyacids (HPAs) (C6H15O2N2)3−xHxPW12O40 (abbreviated as Ly3−xHxPW) have been designed using different ratios of HPAs with amino acid lysine in order to control their acid–base properties. The amino acid group facilitated the HPAs forming micellar assemblies in choline chloride–fructose deep eutectic solvents. In the dehydration of fructose to 5-hydroxymethylfurfural (HMF), Ly3−xHxPW exhibited different catalytic activities because of their different acid–base properties. Among all the HPA catalysts, Ly2HPW gave the best results with 93.3% conversion and 92.3% HMF yield within a very short time, i.e. 1 min under the conventional temperature of 110 °C using choline chloride (ChCl) as solvent, and this was almost the best result by far. The highest activity and selectivity of Ly2HPW came from the synergistic effect between certain acidic and basic capacities, which provides ready accessibility to the nucleophilic (–NH2) and electrophilic (H) sites. Moreover, this catalyst was tolerant to highly concentrated feedstock (∼66.7 wt%) with the additive ChCl. Ly2HPW performed as a heterogeneous catalyst in the ChCl system and could be recycled by simple washing treatment.

Acid–base bifunctional HPA nanocatalysts promoting heterogeneous transesterification and esterification reactions

A new catalytic system including acid–base bifunctional heteropolyacids (HPAs) nanocatalyst is presented, for the simultaneous transesterification of oil and esterification of free fatty acids (FFAs), to directly convert low quality feedstocks to biodiesel in a one-pot process.

Tailoring the Synergistic Bronsted-Lewis acidic effects in Heteropolyacid catalysts: Applied in Esterification and Transesterification Reactions

In order to investigate the influences of Lewis metals on acidic properties and catalytic activities, a series of Keggin heteropolyacid (HPA) catalysts, HnPW11MO39 (M = TiIV, CuII, AlIII, SnIV, FeIII, CrIII, ZrIV and ZnII; for Ti and Zr, the number of oxygen is 40), were prepared and applied in the esterification and transesterification reactions. Only those cations with moderate Lewis acidity had a higher impact. Ti Substituted HPA, H5PW11TiO40, posse lower acid content compared with TixH3−4xPW12O40 (Ti partial exchanged protons in saturated H3PW12O40), which demonstrated that the Lewis metal as an addenda atom (H5PW11TiO40) was less efficient than those as counter cations (TixH3−4xPW12O40). On the other hand, the highest conversion reached 92.2% in transesterification and 97.4% in esterification. Meanwhile, a good result was achieved by H5PW11TiO40 in which the total selectivity of DAG and TGA was 96.7%. In addition, calcination treatment to H5PW11TiO40 make it insoluble in water which resulted in a heterogeneous catalyst feasible for reuse.

Ultra-deep desulfurization via reactive adsorption on peroxophosphomolybdate/agarose hybrids.

A catalyst system composed of peroxophosphomolybdates as catalytic center and agarose as matrix material had been designed. The [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]/agarose (C16PMo(O2)2/agarose) hybrid was found to be active for oxidation desulfurization (ODS) of dibenzothiophene (DBT) or real fuel into corresponding sulfone by H2O2 as an oxidant, while the sulfur content could be reduced to 5ppm. The higher activity comes from its components including [PO4{MoO(O2)2}4] catalytic sites, the hydrophobic quaternary ammonium cation affinity to low polarity substrates, and agarose matrix affinity to H2O2 and sulfone. During the oxidative reaction, the mass transfer resistance between H2O2 and organic sulfurs could be decreased and the reaction rate could increase by the assistance of agarose and hydrophobic tails of [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]. Meanwhile, the oxidative products could be adsorbed by agarose matrix to give clean fuel avoiding the post-treatment. In addition, the hybrid was easily regenerated to be reused.

Fabrication of H3PW12O40/agarose membrane for catalytic production of biodiesel through esterification and transesterification

A membrane reactor containing heteropolyacids was designed by embedding tungstophosphoric acid (H3PW12O40, abbreviated as HPW) onto the lattice of agarose. During the gelation of agarose, HPW molecules were embedded on the densely packed 3D network of agarose through strong interaction between the polyhydroxyl sites of agarose and oxygen from HPW. This avoided the aggregation of HPW molecules and resulted in the equal distribution of HPW in the membrane. Furthermore, a material with as high as 38% loading amount of HPW on agarose had been achieved. The acidic activity was evaluated in the esterification of free fatty acid and transesterification of Eruca Sativa Gars (ESGs) oil with methanol in batch reaction. Among all HPW/agarose, it was found that HPW/agarose membrane with 38 wt% HPW showed the highest efficiency in both reactions under the optimized reaction conditions with TOF values of 82 h−1, and 27.6 h−1 (based on the yield of MP), respectively, in the batch reactor. Then the reaction rates increased to 164 and 45.8 h−1 in the membrane reactor. The solid and tough structure of HPW/agarose confirm its high stability and duration, it could be used at least ten times without significant loss of activity. Furthermore, the reaction rates could be increased at least two fold in membrane mode compared to those in batch mode, showing the separation ability of water or glycerol from the mixture by the HPW/agarose membrane. This is a potential strategy for the production of biodiesel based on heteropolyacid catalysts. The fuel properties of biodiesel from ESG oil showed that they were all satisfactory for the ASTM biodiesel standard.

Hydrolysis and alcoholysis of polysaccharides with high efficiency catalyzed by a (C16TA)xH6−xP2W18O62 nanoassembly

Wells–Dawson structured heteropolyacid (HPA) H6P2W18O62 was first used as a precursor to fabricate a micellar assembly, [C16H33N(CH3)3]xH6−xP2W18O62 (abbreviated as (C16TA)xH6−xP2W18O62). Hydrolysis and methanolysis of polysaccharides including cellobiose, starch, and cellulose were catalyzed by (C16TA)xH6−xP2W18O62. (C16TA)H5P2W18O62 showed the highest activity, with hydrolysis rates of cellobiose, starch and cellulose of 0.74, 0.02, 0.0.8 min−1 at 100 °C, 120 °C and 160 °C, respectively, much better than Keggin H3PW12O40. Meanwhile, (C16TA)H5P2W18O62 performed 94.8% conversion of cellulose into methyl levulinate (MLA) with 58.5% yield in methanol. The high activity of the catalyst was attributed to the synergistic effect of a high concentration of acid, more substrates adsorbed, and the oxidizing ability of (C16TA)H6P2W18O62. The results demonstrated that it was an effective and reusable catalyst for the production of glucose and MLA from polysaccharides.

Heteropolyacids embedded in a lipid bilayer covalently bonded to graphene oxide for the facile one-pot conversion of glycerol to lactic acid

A new two-step strategy for the functionalization of graphene oxide (GO) with heteropolyacids (HPAs) and the catalytic activity of the so-obtained materials in the conversion of glycerol to lactic acid (LA) are reported. Covalent bonding of a a-NH–(CH2)2–NH2+–CH2(CH2)8CH3 lipid-like bilayer to the GO surface is followed by embedding of HPAs to give HPMo@lipid(n)/GO hybrid materials, where n represents the length of the diamine carbon chain (n = 2, 4, 6, 8, and 10). The HPAs are tightly surrounded by the lipid bilayer through electrostatic interactions with the protonated amine groups and are highly resistant to environmental changes and leaching from the GO. The hydrophilicity of HPAs and GO and the hydrophobic properties of the lipid bilayer can be easily controlled by changing the length of the alkyl chain, and the redox potential varies as the distance between HPAs and GO varies. The materials show excellent catalytic activity in glycerol cascade conversion to LA, with HPMo@lipid(4)/GO achieving the highest reported efficiency to date, with 90% yield at 97% conversion under mild conditions (1 M glycerol, 60 °C, 3.5 h, and 10 bar O2). Such high efficiency is attributed to the combination of suitable redox potentials, balanced hydrophilic and hydrophobic properties, and the capillary-like reactor formed by the wall of the lipid bilayer, which enhances the adsorption of O2 and glycerol around catalytic active sites. HPMo@lipid(4)/GO functions in the absence of an organic solvent and base, with a high concentration of glycerol (9.2 wt%) and in the presence of methanol and other impurities from biodiesel production, with crude glycerol giving almost 87% yield. No structural changes or leaching of HPAs from GO occurs during the reaction or with recycling up to fifteen times.

Efficient mineralization of phenol by a temperature-responsive polyoxometalate catalyst under wet peroxide oxidation at lower temperatures

Herein, a temperature-responsive polyoxometalate (POM) catalyst [C16H33(CH3)3N]3[PO4{WO(O2)2}4]/poly(N-isopropylacrylamide) (abbreviated as (C16PW(O2)2/PNIPAM) was prepared and used in the catalytic wet peroxide oxidation (CWPO) of phenol under mild conditions. The POM catalyst C16PW(O2)2/PNIPAM showed a higher degradation efficiency and mineralization of phenol with H2O2 at room temperature or even at lower temperature (0 °C) within a short time (120 min). The high efficiency at lower temperature was attributed to its temperature-responsive property, wherein the lattice of the temperature-sensitive polymer relaxed at lower temperature and then wrinkled at higher temperature. These characteristics also permitted C16PW(O2)2/PNIPAM to be easily separated for recycling. The leaching test indicated that the POM catalyst exhibited excellent stability and little leaching and can be used as a thermosensitive catalyst for about six times. C16PW(O2)2/PNIPAM has potential application in the CWPO of phenol without the limitation of temperature and pH conditions.